The three types of UV radiation are classified according to their wavelength. They differ in their biological activity and the extent to which they can penetrate the skin. The shorter the wavelength, the more harmful the UV radiation. However, shorter wavelength UV radiation is less able to penetrate the skin.

Short-wavelength UVC is the most damaging type of UV radiation. However, it is completely filtered by the atmosphere and does not reach the earth's surface.

Medium-wavelength UVB is very biologically active but cannot penetrate beyond the superficial skin layers. It is responsible for delayed tanning and burning; in addition to these short-term effects it enhances skin ageing and significantly promotes the development of skin cancer. Most solar UVB is filtered by the atmosphere.

The relatively long-wavelength UVA accounts for approximately 95 per cent of the UV radiation reaching the Earth's surface. It can penetrate into the deeper layers of the skin and is responsible for the immediate tanning effect. Furthermore, it also contributes to skin ageing and wrinkling. For a long time it was thought that UVA could not cause any lasting damage. Recent studies strongly suggest that it may also enhance the development of skin cancers

Short-wave ultraviolet radiation, in the “C” band of 200 to 280 nanometers, has been used in a wide range of germicidal applications since the late 1800s to destroy bacteria, mold, yeast, and viruses. UV-C, or UVC, is often referred to as germicidal UV or GUV.  Ultraviolet light in this wavelength renders the organisms sterile. When organisms can no longer reproduce, they die.


What can UV-C Pass through


Short wave ultraviolet light (UV-C) is used to kill bacteria, hasten chemical reactions (as a catalyst), and is also valuable in the identification of certain fluorescent minerals. Unlike long wave UV, the short wave UV cannot pass through ordinary glass or most plastics. The shortest wavelengths cannot even travel very far through the air before being absorbed

The actual life of a UVC light is 10 – 12,000 hours. The useful life is 8-9,000 hours.

This equates to 2 years of continuous usage.


An hour meter can be supplied on the Pureflow product which tracks the hours of use which can be reset.

Yes, UV-C kills living bacteria, but viruses are technically not living organisms; thus, we should correctly say “inactivate viruses.” Individual, energetic UV-C photons photochemically interact with the RNA and DNA molecules in a virus or bacterium to render these microbes non-infectious. This all happens on the microscopic level. Viruses are less than one micrometer (µm, one-millionth of a meter) in size, and bacteria are typically 0.5 to 5 µm.

Yes, if the virus is directly illuminated by UV-C at the effective dose level. UV-C can play an effective role with other methods of disinfection, but it is essential that individuals be protected to prevent UV hazards to the eyes and skin. UV-C should not be used to disinfect the hands!

The official position of the World Health Organization (WHO) is that this virus is spread by contact with large respiratory droplets, directly or indirectly by touching contaminated surfaces and then touching the eyes, nose, or mouth. However, research is underway to determine the degree of airborne spread—meaning virus in particles so small that they remain suspended in air. Such aerosol results from the evaporation of larger respiratory particles generated by coughs, sneezes, ordinary speech, singing, and possibly by faulty plumbing systems, as occurred with the severe acute respiratory syndrome (SARS) virus. How much of the virus responsible for COVID-19 is spread by the airborne route is not clear, but recommendations for healthcare workers to use fitted respirators, not surgical masks, reveal official concern for airborne transmission. The possibility that inhaled virus may result in more-severe lung damage than acquisition by other routes—for example, via the mouth, nose, or eye—is currently being investigated.


Yes. Some hospitals have used portable UV-C fixtures to disinfect air and surfaces in unoccupied, locked rooms as a supplemental control measure to reduce the spread of healthcare associated infections.[6] However, well controlled studies of efficacy are very difficult to conduct and therefore lacking. Medical treatment facilities are using GUV in three primary ways: 1) upper-room UV-C fixtures with air mixing, for controlling airborne pathogens in an occupied spaces, such as the Purelight Flow 2) mobile UV-C units, to disinfect high-touch surfaces, such as the Purelight Hybrid and 3) UV-C in HVAC air handling units, to treat recirculated air and to reduce mold growth on cooling coils. Autonomous (“robot”) systems have been used in some U.S. hospitals and were used in the People’s Republic of China in response to COVID-19.[7] In fighting a war, which this is seen to be, a single weapon is never used; rather, multiple weapons in the armamentarium are exploited.[8] There is no reason not to make full use of UV-C with appropriate precautions in this “war” against COVID-19.

While UV-C could be a secondary infection control measure for disinfecting potential germ-carrying deposits on accessible (not-shadowed) surfaces, its great value would be in disinfecting air in areas where this may be a concern (e.g., intensive care wards, hospital intake facilities [or tents]). Upper-air GUV is the safest, most effective application of UV-C. In special locations, where viral transmission is highly likely, whole-room UVGI (from suspended fixtures directing UV-C downward) could be applied, provided strict precautions can be followed. It is critical that any persons remaining in the space being disinfected from overhead and side UV-C lamps wear protective clothing and eye protection, or exposure to harmful UV will occur. Whole-room GUV has been safely applied in unoccupied rooms where entry is forbidden during the UVGI.

This is important, but difficult to answer in a simple fashion and it depends on how the microbes were made airborne, e.g., from a sneeze or cough, or by being blown up from surfaces or dusted off clothes. The smallest particles (1- to 5-µm droplet nuclei) can remain airborne much longer than cough droplets—for many minutes or even hours.


Are UV-C Lamps safe?


UVGI lamp emissions can pose a workplace safety and health hazard to the eyes and skin if the lamps are improperly used or installed. However, these lamps can be used safely if workers are informed regarding the hazards and follow appropriate precautions. Upper-room GUV has been safely used for preventing airborne transmission for at least 70 years. A great deal is known about the human exposure limits of 254-nm UV (UV-C) irradiation. Compared to the UV-A and UV-B in sunlight, UV-C is almost entirely absorbed by the outer dead layer (stratum corneum) and outer skin (outer epidermis), with very limited penetration to the deeper cellular layers of skin where new cells are constantly created. For comparison, the current daily safety limit of 254-nm UV-C for 8 hours is 6.0 mJ/cm2, whereas less than ten minutes of summer sun exposure at a UV Index of 10 can deliver the equivalent limiting daily safety dose[17] because of its much more-penetrating UV-A and UV-B. A study of continuous monitoring of healthcare workers and patients in an upper-air GUV installation recorded no more than 1/3 of the 8-hour dose. Because it has no outer dead protective layer, the human eye is the organ most susceptible to sunlight and upper-room GUV. Exceeding the threshold level value (TLV) in the lower room will result in painful irritation of the cornea similar to overexposure on a sunny day, especially from sun reflected from water or snow. The damage is painful but transitory, with corneal shedding and replacement in a day or two. When the UV-C source is overhead, the eyes receive very little exposure during normal activities; this is demonstrated in sunlight when the sun is overhead—there is hazardous exposure of the skin but not the eyes. There are no known long-term consequences from an accidental UV-C overexposure.[18] Most eye injuries result from workers on ladders cleaning fixtures or working in the upper room without first turning off the fixtures.[19] For this reason, only trained maintenance workers should be working in the upper room or replacing in-duct lamps. Eye injuries have resulted from insufficient training or improper installation—e.g., workers mistakenly installing an upper-room UVGI fixture upside-down after bulb replacement.[20]

[17] American Conference of Governmental Industrial Hygienists. 2020 Threshold Limit Values and Biological Exposure Indices. Cincinnati: ACGIH; 2020.

[18] International Commission on Illumination (CIE). CIE 187:2010, UV-C Photocarcinogenesis Risks from Germicidal Lamps. Vienna: CIE; 2010.

[19] Sliney D. Balancing the risk of eye irritation from UV-C with infection from bioaerosols. Photochem Photobiol. 2013;89(4):770-6. [Erratum in: Photochem Photobiol. 2013 Jul-Aug; 89(4):770].

[20] Sensakovic JW, Smith LG. Nosocomial ultraviolet keratoconjunctivitis. Infect Control. 1982;3:475-6.


Will UV-C rays increase my lifetime risk of skin cancer?

UV-C penetrates only the superficial layers of the skin and eye, with the shortest wavelengths hardly penetrating at all to living cells (epidermis), so only a very mild, transitory “sunburn” (erythema) occurs from accidental over-exposure of skin areas. Even though GUV lamps can pose a theoretical delayed hazard, incidental UV exposures in the workplace would not significantly increase one’s lifetime risk for cataract or skin cancer when compared to daily exposure to the UV radiant energy in sunlight. Solar UV is much more penetrating and reaches the germinative (new-cell producing) layers in the skin, with the result that skin cancer risk is significant, and sunburns can be severe. There is a small amount of UV-B (297, 303, 313 nm) from a low-pressure mercury lamp, but this is insignificant unless exposures are experienced at least an order of magnitude or more above the safety limits for 254 nm.[18]

[18] International Commission on Illumination (CIE). CIE 187:2010, UV-C Photocarcinogenesis Risks from Germicidal Lamps. Vienna: CIE; 2010.